#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;
double m, y, s;
int t;
int out(double k)
{
    printf("%.1f", k * 100);
    exit(0);
}
void solve(double l, double r)
{
    double k = (l + r) / 2, u = r - l;
    double a = m;
    if (u < 0.0001) out(k);
    for (int i = 1; i <= t; i++)
        a = a * (1 + k) - y;
    if (a > 0) solve(l, k);
    if (a < 0) solve(k, r);
    if (a == 0) out(k);
}
int main()
{
    cin >> m >> y >> t;
    solve(0, 5);
}